1. Field of the Invention
The present invention relates to an image sensor and an image capturing apparatus using it.
2. Description of the Related Art
There is proposed an image capturing apparatus which performs focus detection by, as a method for detecting the focus state of a photographing lens, a pupil division phase-difference method (imaging plane phase-difference method) using a two-dimensional image sensor in which a microlens is formed in each pixel.
U.S. Pat. No. 4,410,804 discloses an image capturing apparatus using a two-dimensional image sensor in which one microlens and a plurality of divided photo-electric conversion units are formed for one pixel. The divided photo-electric conversion units are configured to receive beams having passed through different areas of the exit pupil of a photographing lens through one microlens, thereby achieving pupil division. Focus detection is performed by obtaining an image shift amount from signals of the beams received by the divided photo-electric conversion units. An imaging signal is acquired by adding the signals of the beams received by the divided photo-electric conversion units. In addition to focus detection, U.S. Pat. No. 4,410,804 discloses that a stereoscopic image can be provided by separately displaying, for the right and left eyes, parallax signals of beams received by right and left divided photo-electric conversion units in each pixel.
In focus detection by the pupil division phase-difference method using the two-dimensional image sensor, the focus detection accuracy greatly depends on the pupil intensity distribution (pupil division performance) of focus detection pixels. High-accuracy focus detection can be implemented by setting a high peak intensity of the pupil intensity distribution of focus detection pixels and setting a narrow half-value width.
However, if a light guide is formed between the microlens and a plurality of divided photo-electric conversion units to increase the light receiving efficiency at a small pixel size of the image sensor, this impairs the pupil division performance.